Single or multi-layer printed circuit board with improved via design

ABSTRACT

A circuit board or each circuit board of a multi-layer circuit board includes an electrically conductive sheet coated with an insulating top layer covering one surface of the conductive sheet, an insulating bottom layer covering another surface of the conductive sheet and an insulating edge layer covering an edge of the conductive sheet. An insulating interlayer can be sandwiched between a pair of adjacent circuit boards of a multi-layer circuit board assembly. A landless through-hole or via can extend through one or more of the circuit boards for connecting electrical conductors on opposing surfaces thereof.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part (CIP) of U.S. patentapplication Ser. No. 10/227,768, filed Aug. 26, 2002, entitled “SingleOr Multi-Layer Printed Circuit Board With Recessed Or Extended BreakawayTabs And Method Of Manufacture Thereof”, which is incorporated herein byreference, which is a CIP of U.S. patent application Ser. No.10/184,387, filed Jun. 27, 2002, entitled “Process For Creating Vias ForCircuit Assemblies”, which is also incorporated herein by reference.

BACKGROUND OF THE INVENTION

Presently, printed circuit boards are fabricated as part of a largerpanel. Each printed circuit board can be configured in any shape,although most printed circuit boards in common use are made inrectangular shapes of standard sizes. When fabrication of a printedcircuit board is complete, it is cut and separated from the largerpanel, mostly by way of a machine cutting or routing process in which achannel is cut around the printed circuit board. In certain designs, thechannel around the printed circuit board does not completely encirclethe perimeter of the printed circuit board. Rather, tabs are left atseveral places around the perimeter of the printed circuit board toattach it to the larger panel until the board is singulated from thelarger panel by breaking the tabs. Typically, metal planes in theprinted circuit board do not extend to its edge where they would be cutby the routing process. In this way, no conductive metal is left exposedon the edges of the printed circuit board.

The existing methods of cutting printed circuit boards from largerpanels are unsatisfactory for high density boards because the limiteddimensional stability of the printed circuit boards does not allowregistration of one high density pattern to the next on the largerpanel. Cut lines made around the periphery of the printed circuit boardfurther weaken the panel material, exasperating misregistration of onepattern to the next.

Electronic systems assembled onto conventional printed circuit boardsrely upon thermal conduction from integrated circuits dissipating heatto the printed circuit board to remove some of the heat from theintegrated circuits. For intermediate ranges of heat, up to about 2watts per chip, conduction to the printed circuit board is sufficient tocool the integrated circuits without the need for bulky and expensiveheat sinks. In high performance systems, however, as the density of thesystem and the percentage of the substrate covered by the integratedcircuits increases, the thermal path to the printed circuit board isless efficient. At a point when the density of the system increasessufficiently, the printed circuit board is not effective as a heat sinkfor the integrated circuits. However, the need for effective thermalconduction from the integrated circuits to the substrate and therefromto the ambient becomes more important as system density increases.Because of the evolution toward higher system density and largerintegrated circuit coverage, means are needed for cooling the substratein order to maintain the integrated circuits on the substrate at a safeoperating temperature.

In addition to thermal conduction, high performance systems increasinglyrequire low impedance power and ground voltage supplies to run theintegrated circuits at high clock speeds. Typically, the AC impedancesof power and ground supplies are lowered by the use of low impedancebypass capacitors connected to the power and ground planes. Onconventional printed circuit boards, capacitors are connected to powerand ground planes through vias which extend through some thickness ofthe board, increasing the impedance of this contact and degradingperformance of the system. As switching speeds increase, the problem ofmaking low impedance connections between bypass capacitors and the powerand ground planes becomes more important.

It would, therefore, be desirable to overcome the above problems andothers by providing a printed circuit board having one or more printedcircuit board layers each of which has a conductive layer which extendsto the edge thereof and which is substantially, but not completely,covered by an insulating material. The edge of the conductive layer notcovered by the insulating material can be on the perimeter (or edge) ofthe printed circuit board layer or on the edge of a tab which isutilized to couple the board to a disposable part of a larger panel thatthe board is formed from during fabrication. The exposed edge of theconductive layer becomes exposed upon singulating the printed circuitboard layer from each tab connected thereto or upon breaking the tabduring singulation of the printed circuit board from the disposable partof the larger panel. In one embodiment, the broken end of one or moretabs terminate in a recess in the perimeter of the printed circuitboard. In a second embodiment, the broken end of one or more tabs extendoutward from the perimeter of the printed circuit board.

The conductive plane can be formed from metal that can serve the dualpurpose of conducting heat away from electrical components disposed onone or both surfaces of the printed circuit board or printed circuitboard layer and for providing power or ground to the electricalcomponents. The tab which extends outward from the edge of the secondembodiment printed circuit board can be coupled to a mechanical fixtureand/or an electrical fixture to provide a path for the flow of heat fromthe printed circuit board to externally coupled mechanical fixturesand/or to provide electrical power to the electrically conducting layerof the printed circuit board.

Each printed circuit board layer can include one or more landlessthrough-holes or vias extending all or part of the way therethrough.Each landless through-hole or via is desirably configured to facilitatethe deposition of conductive material therein, the patterning andetching of said conductive material and the formation of thethrough-hole or via without a conductive land on each exposed endthereof.

SUMMARY OF THE INVENTION

The invention is a multi-layer printed circuit board that is formed froma plurality of printed circuit boards (PCB) that have been laminatedtogether. Each PCB includes an electrically conductive sheet coated withan insulating top layer covering one surface of the conductive sheet, aninsulating bottom layer covering another surface of the conductivesheet, an insulating edge layer covering an edge of the conductive sheetand a circuit pattern defined on an outward facing surface of at leastone of the top layer and bottom layer. An insulating interlayer issandwiched between a top layer of a first PCB of the plurality of PCBsand a bottom layer of a second PCB of the plurality of PCBs.

The insulating edge layer can include at least one opening where atleast part of the edge of the conductive sheet is exposed.

At least one electrical conductor, such as, without limitation, aconductive post, can electrically connect the circuit patterns on thefirst and second PCBs by way of the insulating interlayer.

The circuit pattern of one of the PCBs can include at least oneelectrical conductor on the top layer of the one PCB and at least oneelectrical conductor on the bottom layer of the one PCB. A through-holeor via can extend through the one PCB. The through-hole can have anelectrical conducting interior surface extending therethroughelectrically connecting the one electrical conductor on the top layer ofthe one PCB and the one electrical conductor on the bottom layer of theone PCB. The electrical conducting interior surface can be electricallyisolated from the electrically conductive sheet by an insulatingthrough-hole layer.

The interior surface of the through-hole can converge from a positionadjacent the top layer of the one PCB to a position intermediate the toplayer and the bottom layer of the one PCB and can diverge from theposition intermediate the top layer and the bottom layer of the one PCBto a position adjacent the bottom layer of the one PCB.

In cross section, one side of the interior surface of the through-holecan have an arcuate outline from the position intermediate the top layerand the bottom layer to either the position adjacent the top layer orthe position adjacent the bottom layer. In cross section, opposing sidesof the interior surface of the through-hole can have an outlinegenerally in the shape of a hyperbola.

The circuit pattern of one of the PCBs can include a plurality ofelectrical conductors on the top layer of the one PCB and a plurality ofelectrical conductors on the bottom layer of the one PCB. A through-holeor via can extend through the one PCB. The through-hole can have aplurality of through-hole conductors extending therethrough. Eachthrough-hole conductor can be electrically isolated from each otherthrough-hole conductor by the insulating through-hole layer which isdisposed between the electrically conductive sheet and the plurality ofthrough-hole conductors. Each through-hole conductor can be electricallyconnected to at least one electrical conductor on the top layer of theone PCB and/or to at least one electrical conductor on the bottom layerof the one PCB.

An interior surface of the through-hole can converge from a positionadjacent the top layer of the one PCB to a position intermediate the toplayer and the bottom layer of the one PCB and can diverge from theposition intermediate the top layer and the bottom layer of the one PCBto a position adjacent the bottom layer of the one PCB.

In cross section, one side of the interior surface of each through-holeconductor or one side of the interior surface of the insulatingthrough-hole layer disposed between a pair of through-hole conductorscan have an arcuate outline from the position intermediate the top layerand the bottom layer to either the position adjacent the top layer orthe position adjacent the bottom layer. More specifically, the crosssection of the one side of the interior surface of the through-holeconductor or the one side of the interior surface of the insulatingthrough-hole layer can have an outline generally in the shape of oneside of a hyperbola.

The invention is also a method of forming a multi-layer circuit boardcomprising (a) providing a plurality of circuit boards, each circuitboard comprising an electrically conductive sheet conformally coatedwith an insulating material; (b) forming a first circuit on one of thecircuit boards; (c) forming a second circuit on another of the circuitboards; and (d) laminating the plurality of circuit boards together withan insulating interlayer disposed between the one circuit board and theother circuit board and with the first and second circuits electricallyconnected by way of the insulating interlayer.

Each circuit can include at least one conductor. The conformally coatedinsulating material can include at least one opening where at least partof an edge of the conductive sheet is exposed. The at least part of theedge of the conductive sheet can be on a tab that extends from thecircuit board either within or outside a perimeter of the circuit board.

The method can include conformally coating a through-hole or via in theconductive sheet of the one circuit board with the insulating material.At least one through-hole conductor can be formed on at least a portionof the conformally coated insulating material in the through-hole. Theone through-hole conductor can be electrically connected to at least oneconductor of the first circuit formed on one side of the first circuitboard and/or to at least one conductor of the one circuit formed on theother side of the one circuit board.

The method can also include forming a plurality of electrically isolatedthrough-hole conductors on the conformally coated insulating material inthe through-hole. Each through-hole conductor can be electricallyconnected to at least one conductor of the first circuit formed on oneside of the first circuit board and/or to at least one conductor of thefirst circuit formed on the other side of the first circuit board.

An interior surface of the through-hole can converge from a positionadjacent a top surface of the one circuit board to a positionintermediate the top surface and the bottom surface of the one circuitboard and can diverge from the position intermediate the top surface andthe bottom surface of the one circuit board to a position adjacent thebottom surface of the one circuit board.

In cross section, one side of the interior surface of the through-holecan have an arcuate outline from the position intermediate the topsurface and the bottom surface to either the position adjacent the topsurface or the position adjacent the bottom surface. More specifically,the cross section of the one side of the interior surface of thethrough-hole can have an outline generally in the shape of one side of ahyperbola.

The invention is also a circuit board that includes an electricallyconductive sheet coated with an insulating top layer covering onesurface of the conductive sheet, an insulating bottom layer coveringanother surface of the conductive sheet and an insulating edge layercovering an edge of the conductive sheet. The top layer of the circuitboard can include an electrical conductor and the bottom layer of thecircuit board can include an electrical conductor. A through-hole or viacan extend through the circuit board. The through-hole can include athrough-hole conductor extending therethrough electrically connectingthe electrical conductor on the top layer and the electrical conductoron the bottom layer. The through-hole conductor can be electricallyisolated from the electrically conductive sheet by an insulatingthrough-hole layer.

The insulating edge layer can include at least one opening where atleast part of the edge of the conductive sheet is exposed.

An interior surface of the through-hole can converge from a positionadjacent the top layer of the circuit board to a position intermediatethe top layer and the bottom layer of the circuit board and can divergefrom the position intermediate the top layer and the bottom layer of thecircuit board to a position adjacent the bottom layer of the circuitboard.

In cross section, one side of the interior surface of the through-holecan have an arcuate outline from the position intermediate the top layerand the bottom layer to either the position adjacent the top layer orthe position adjacent the bottom layer. More specifically, in crosssection, opposing sides of the interior surface of the through-hole canhave an outline generally in the shape of a hyperbola.

The top layer of the circuit board can include a plurality of electricalconductors and the bottom layer of the circuit board can include aplurality of electrical conductors. The through-hole can include aplurality of through-hole conductors extending therethrough. Eachthrough-hole conductor can be electrically isolated from each otherthrough-hole conductor. Each through-hole conductor can be electricallyconnected to at least one electrical conductor on the top layer and/orto at least one electrical conductor on the bottom layer.

An interior surface of the through-hole can converge from a positionadjacent the top layer of the circuit board to a position intermediatethe top layer and the bottom layer of the circuit board and can divergefrom the position intermediate the top layer and the bottom layer of thecircuit board to a position adjacent the bottom layer of the circuitboard.

In cross section, one side of the interior surface of the through-holecan have an arcuate outline from the position intermediate the top layerand the bottom layer to either the position adjacent the top layer orthe position adjacent the bottom layer. More specifically, the one sideof the cross section of the interior surface of the through-hole canhave an outline generally in the shape of one side of a hyperbola.

Lastly, the invention is a method of forming a circuit board comprising(a) providing a circuit board having a through-hole or via therethrough;(b) conformally coating the electrically conductive sheet, including aninterior surface of the through-hole, with an insulating material; (c)forming a conductor on one side of the conformally coated electricallyconductive sheet; (d) forming another conductor on the other side of theconformally coated electrically conductive sheet; and (e) forming athrough-hole conductor on the insulating material in the through-hole,the through-hole conductor electrically connecting the conductor on theone side of the conformally coated electrically conductive sheet and theconductor on the other side of the conformally coated electricallyconductive sheet.

Step (c) can include forming a plurality of conductors on the one sideof the conformally coated electrically conductive sheet. Step (d) caninclude forming a plurality of conductors on the other side of theconformally coated electrically conductive sheet. Step (e) can includeforming a plurality of through-hole conductors on the insulatingmaterial in the through-hole. Each through-hole conductor can beelectrically isolated from each other through-hole conductor. Eachthrough-hole conductor can be electrically connected to at least oneconductor on the one side of the conformally coated electricallyconductive sheet and at least one conductor on the other side of theconformally coated electrically conductive sheet.

The conformally coated insulating material can include at least oneopening where at least part of an edge of the conductive sheet isexposed. The at least part of the edge of the conductive sheet can be ona tab that extends from the circuit board either within or outside aperimeter of the circuit board.

An interior surface of the through-hole can converge from a positionadjacent the one side of the conformally coated electrically conductivesheet to a position intermediate the one side and the other side of theconformally coated electrically conductive sheet and can diverge fromthe position intermediate the one side and the other side of theconformally coated electrically conductive sheet to a position adjacentthe other side of the conformally coated electrically conductive sheet.

In cross section, one side of the interior surface of the through-holecan have an arcuate outline from the position intermediate the one sideand the other side to either the position adjacent the one side or theposition adjacent the other side. More specifically, one side of thecross section can have an outline generally in the shape of one side ofa hyperbola.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway perspective view of a printed circuit board layerhaving a perforate conductive plane surrounded by an insulating materialin accordance with the present invention;

FIG. 2 is a cutaway perspective view of a portion of a printed circuitboard layer of the type shown in FIG. 1 including a circuit patternformed on the outward facing surfaces thereof;

FIGS. 3 and 4 are plan views of panels having different circuit boardlayers formed therefrom in accordance with the present invention;

FIG. 5 is a plan view of the panels shown in FIGS. 3 and 4 laminatedtogether with the circuit board layers thereof in registry;

FIG. 6 is an isolated plan view of a tab which the panels in FIGS. 3 and4 utilize to connect their circuit board layers to disposable parts ofthe panels;

FIG. 7 is an isolated plan view of the tab shown in FIG. 6 afterbreaking in response to the application of a breaking force appliedthereto;

FIG. 8 is a view taken along lines VIII-VIII in FIG. 7;

FIGS. 9 and 10 are plan views of panels including printed circuit boardlayers in accordance with the present invention;

FIG. 11 is a plan view of the panels shown in FIGS. 9 and 10 laminatedtogether with the circuit board layers thereof in registry;

FIG. 12 is a plan view of the laminated printed circuit board layersshown in FIG. 11 singulated from the disposable parts of theirrespective panels;

FIG. 13 is a section taken along lines XIII-XIII in FIG. 12;

FIG. 14 is a plan view of the singulated laminated circuit board layersshown in FIG. 12 with certain tabs thereof coupled to a mounting fixtureand with certain tabs thereof coupled to an electrical fixture;

FIG. 15 is a cross sectional side view of the laminated printed circuitboard layers of FIG. 12 including an optional insulating interlayerdisposed therebetween and with an exemplary conductor disposed throughthe insulating interlayer for electrically connecting circuit patternson the respective printed circuit board layers;

FIG. 16 is a plan view of an isolated section of a printed circuit boardlayer in accordance with the present invention including a landlessthrough-hole (or via) having a single through-hole conductor therein;

FIG. 17 is a section taken along lines XVII-XVII in FIG. 16;

FIG. 18 is a plan view of a printed circuit board layer in accordancewith the present invention including a landless through-hole (or via)having a plurality of through-hole conductors therein; and

FIG. 19 is a section taken along lines XIX-XIX in FIG. 18.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a printed circuit board layer 2 includes anelectrically conductive sheet or foil 4. Sheet 4 can be formed from acopper foil, an iron-nickel alloy, or combinations thereof. Sheet 4 canbe a perforate sheet as shown in FIG. 1 or can be a solid sheet. It isdesirable for sheet 4 to have a coefficient of thermal expansioncomparable to that of silicon materials from which integrated circuitsare typically prepared in order to prevent failure of adhesion jointsutilized to adhere the integrated circuit or a packaged integratedcircuit (not shown) to printed circuit board layer 2. Describing sheet 4as perforate means that sheet 4 is a mesh sheet having a plurality ofthrough-holes or vias 6 spaced at regular intervals.

An electrically insulative coating 8 is formed around sheet 4. Thiscoating 8 can be formed around sheet 4 in any manner known in the art,such as conformal coating. More specifically, coating 8 forms aninsulating top layer 10 which covers a top surface 12 of sheet 4, aninsulating bottom layer 14 which covers a bottom surface 16 of sheet 4and an insulating edge layer 18 which covers an edge 20 of sheet 4. Whensheet 4 is coated with coating 8, an interior surface of eachthrough-hole or via 6 is also coated with coating 8. Thus, no portion ofsheet 4 is left uncovered by coating 8.

With reference to FIG. 2, and with continuing reference to FIG. 1,printed circuit board layer 2 formed in the above-described manner canhave a conductive pattern formed on the outward facing surface of toplayer 10 and/or the outward facing surface of bottom layer 14 byconventional processes. Specifically, utilizing one or morephotolithographic techniques and one or more metallization techniques,the conductive pattern can be formed on the outward facing surface oftop layer 10 and/or the outward facing surface of bottom layer 14. Thisconductive pattern can include un-plated through-holes or vias 6-1,plated, blind through-holes or vias 6-2, and/or plated through-holes orvias 6-3. Additional details regarding formation of printed circuitboard layer 2 and for forming a conductive pattern, including one ormore of the various types of through-holes or vias 6, on top layer 10and/or bottom layer 14 can be found in U.S. patent application Ser. No.10/184,387, filed Jun. 27, 2002, entitled “Process For Creating Vias ForCircuit Assemblies” which is assigned to the same Assignee as thepresent application and which is incorporated herein by reference.

The preparation of one or more printed circuit board layers 2 in a panelform and the assembly of plural printed circuit board layers to form amulti-layer printed circuit board assembly will now be described.

With reference to FIG. 3, one or more first printed circuit board (PCB)layers 30 are fabricated as part of a panel 32. Each first PCB layer 30is surrounded by a disposable part 34 of panel 32. In accordance withthe present invention, each first PCB layer 30 is coupled to disposablepart 34 of panel 32 by one or more tabs 36.

The general steps to prepare panel 32 to the form shown in FIG. 3 willnow be described. Initially, a first conductive sheet, like conductivesheet 4, of the size of panel 32 is provided. This sheet can either be asolid sheet or a perforate sheet depending on the application. Next, cutlines or slots 38 are formed in the conductive sheet by pattern etchingor a machine cutting or routing process to define the perimeter of eachfirst PCB layer 30 of panel 32. These slots 38 are interrupted by tabs36 which hold each first PCB layer 30 to disposable part 34 duringprocessing.

Next, an electrically insulative coating, like coating 8, is depositedon the conductive sheet forming panel 32 in a manner whereupon the topsurface, the bottom surface, and the edges of the electricallyconductive sheet associated with each first PCB layer 30 that wereexposed during the formation of slots 38 are covered thereby. If theconductive sheet is perforate, the electrically insulative coating alsocovers the interior surface of each through-hole or via. In addition,the top and bottom surfaces and the edges of each tab 36 defined duringthe formation of slots 38 can also be covered by the electricallyinsulative coating. The top and bottom surfaces and the edges ofdisposable part 34 defined during formation of slots 38 can also becovered with the electrically insulative coating. However, this is notrequired. Typically, however, all of the edges, surfaces and, if viasare provided, the interior surface of each via of the conductive sheetof panel 32 are covered by the electrically insulative coating.

Next, photolithographic processing techniques and metallizationtechniques known in the art and described in the above-identified UnitedStates patent application incorporated herein by reference are utilizedto define a circuit pattern 40 on one or both of the exposed surfaces ofthe electrically insulative coating deposited on the portion of theelectrically conductive sheet associated with each first PCB layer 30.

If each first PCB layer 30 is ready for use after circuit pattern 40 isformed thereon, each first PCB layer 30 can be singulated from panel 32by applying a breaking force to each tab 36 connecting each first PCBlayer 30 to disposable part 34. However, if desired, one or moreadditional layers of electrically insulative coating (not shown) andcircuit patterns (not shown) can be formed over circuit pattern 40, withthe various layers of circuit patterns interconnected in a desiredmanner utilizing conventional processes. Thereafter, each first PCBlayer 30 can be singulated from panel 32 by applying a breaking force toeach tab 36 connecting each first PCB layer 30 to disposable part 34. Ifthe breaking force is applied to each tab 36 at the perimeter (or edge)of first PCB layer 30, i.e., at the boundary between tab 36 and firstPCB layer 30, a portion of the edge of first PCB layer 30 where said tabwas connected becomes exposed. More specifically, separating each tab 36from first PCB layer 30 at the perimeter thereof exposes a portion ofthe edge of the conductive sheet of first PCB layer 30 where said tab 36was previously connected.

Alternatively, each first PCB layer 30 of panel 32 can be laminated to asecond PCB layer 42 of a panel 44 shown in FIG. 4. Panel 44 includes oneor more second PCB layers 42 connected to a disposable part 46 of panel44 by tabs 48 defined during formation of slots 50 in the electricallyconductive sheet of panel 44 in the same manner described above inconnection with the formation of slots 38 in panel 32.

An electrically insulative coating is deposited on the conductive sheetforming panel 44 in a manner whereupon the top surface, the bottomsurface and the edges of electrically conductive sheet associated witheach second PCB layer 42 that were exposed during the formation of slots50 are covered thereby. If the conductive sheet is perforate, theelectrically insulative coating also covers the interior surface of eachthrough-hole or via. In addition, the top and bottom surfaces and theedges of each tab 48 defined during the formation of slots 50 can alsobe covered by the electrically insulative coating. The top and bottomsurfaces and the edges of disposable part 46 defined during formation ofslots 50 can also be covered with the electrically insulative coating.However, this is not required. Typically, however, all of the edges,surfaces and, if vias are provided, the interior surface of each via ofthe conductive sheet of panel 44 are covered by the electricallyinsulative coating.

Each second PCB layer 42 has a circuit pattern 52 formed on one or bothof the exposed surfaces of the electrically insulative coating depositedon the portion of the electrically conductive sheet associated with eachsecond PCB layer 42. If desired, each second PCB layer 42 can includeone or more additional layers of electrically insulative coating andcircuit patterns formed over circuit pattern 52, with the various layersof circuit patterns interconnected in the desired manner utilizingconventional processes.

With reference to FIG. 5, and with ongoing reference to FIGS. 3 and 4,panels 32 and 44 can be laminated together in a manner known in the art,with each first PCB layer 30 positioned in registry with a correspondingsecond PCB layer 42 to form a multi-layer PCB assembly 60. Appropriatetechniques known in the art can be utilized to form one or moreelectrical connections between circuit pattern 40 and circuit pattern52. For simplicity of description, the formation of these one or moreelectrical connections between circuit pattern 40 and circuit pattern 52will not be described herein.

As shown best in FIG. 5, tabs 36 of panel 32 do not overlay tabs 48 ofpanel 44 when panels 32 and 44 are laminated together. In this manner,PCB layers 30 and 42 forming each multi-layer PCB assembly 60 can besingulated from their disposable parts 34 and 46, respectively,independent of each other. If desired, however, one or more tabs 36 and48 can be in alignment with each other when panels 32 and 44 arelaminated.

Each second PCB layer 42 can be singulated from panel 44 by applying abreaking force to each tab 48 connecting each second PCB layer 42 todisposable part 46. The breaking force applied to each tab 48 can beapplied at the perimeter (or edge) of the corresponding second PCB layer42, i.e., at the boundary between tab 48 and second PCB layer 42,thereby exposing a portion of the edge of second PCB layer 42 and, moreparticularly, a portion of the edge of the conductive sheet of secondPCB layer 42 where said tab 48 was previously connected.

With reference to FIGS. 6 and 7, and with continuing reference to FIGS.3-5, alternatively, instead of breaking one or more tabs 36 and 48 atthe perimeter (or edge) of the corresponding first PCB layer 30 andsecond PCB layer 42, respectively, one or more of tabs 36 and 48 can beconfigured to break intermediate the ends thereof to facilitatesingulation of the corresponding PCB layers 30 and 42 from thecorresponding disposable parts 34 and 46. If desired, the position whereeach such tab 36 and 48 is configured to break can be received within arecess of the corresponding PCB layer whereupon, after breakage, noportion of the tab remaining attached to the PCB layer extends outside aperimeter of the PCB layer. Each such tab 36 and 48 will now bedescribed with respect to an exemplary tab 36 of panel 32. However, itis to be appreciated that each tab 48 of panel 44 is similar to each tab36 of panel 32 and, therefore, the following description of exemplarytab 36 is applicable to each tab 48.

As shown in FIG. 6, exemplary tab 36 extends between first PCB layer 30and disposable part 34. To facilitate breaking, exemplary tab 36includes a narrowing 62, also known as a Charpy notch, along its length.This narrowing 62 enables exemplary tab 36 to break at a well-definedposition whereupon exemplary tab 36 separates into a first part 64 thatremains attached to first PCB layer 30 and a second part 66 that remainsattached to disposable part 34.

The ends of slots 38 on opposite sides of exemplary tab 36 define arecess 68 within a perimeter 70 of first PCB layer 30. For purpose ofthe present description, perimeter 70 of first PCB layer 30 includes theouter edge 72 of first PCB layer 30 and the imaginary extension 74 ofouter edges 72 across each recess 68. As shown, the narrowing 62 of eachtab 36 is within perimeter 70 of first PCB layer 30. Hence, whenexemplary tab 36 separates into first part 64 and second part 66, adistal end 76 of each first part 64 terminates within recess 68.

With reference to FIG. 8, and with continuing reference to all previousFigs., since first PCB layer 30 and exemplary tab 36 include anelectrically conductive sheet 78, like sheet 4 in FIG. 1, coated with anelectrically insulative coating 80, like coating 8 in FIG. 1, breakingexemplary tab 36 exposes a small portion 82 of the edge of electricallyconductive sheet 78 and the surrounding electrically insulative coating80. Since only the distal end 76 of first part 64 of exemplary tab 36includes small portion 82 of electrically conductive sheet 78 exposed,substantially all of the edge of electrically conductive sheet 78 iscovered by electrically insulative coating 80 and, more particularly,the insulating edge layer of electrically insulative coating 80.Accordingly, inadvertent electrical contact with the edge ofelectrically conductive sheet 78 covered with the insulating edge layerof electrically insulative coating 80 is avoided.

The electrically conductive sheet of first PCB layer 30 and second PCBlayer 42 can be utilized to conduct heat away from electrical componentsdisposed on one or both surfaces thereof. In addition, the electricallyconductive sheets of PCB layers 30 and 42 of each multi-layer PCBassembly 60 can be utilized to provide power and ground to electricalcomponents disposed on the outward facing surfaces of multi-layer PCBassembly 60. This is accomplished by connecting the power lead of eachintegrated circuit disposed on multi-layer PCB assembly 60 to theconductive sheet of one PCB layer 30 and 42 and connecting the groundlead of each integrated circuit to the conductive sheet of the other PCBlayer 30 and 42. The conductive sheet of each PCB layer 30 and 42 canthen be connected to an appropriate one of a power terminal and a groundterminal of an external power supply via the small portion 82 of theedge of the electrically conductive sheet exposed on the first part 64of one or more tabs 36 by suitable fixture means.

With reference to FIG. 9, a first PCB layer 90 can be fabricated in thesame manner as first PCB layer 30 discussed above in connection withFIG. 3. One or more tabs 92 can extend outward from a perimeter 94 offirst PCB layer 90 and connect it to a disposable part 96 of a panel 98that also includes first PCB layer 90 and tab 92. In a manner similar toPCB layers 30 and 42 and tabs 36 and 48, respectively, first PCB layer90 and tabs 92 can be formed from an electrically conductive sheethaving its top and bottom surfaces and edges coated with an electricallyinsulative coating. However, the electrically insulative coating can beomitted from one or more tabs 92 or can be removed from one or more tabs92 after deposit. One or more of tabs 92 can each include a mountinghole 100 that can be utilized to couple tab 92 to mounting hardware orexternal electrical circuitry, such as a power supply.

A circuit pattern 101 can be formed on one or both exposed surfaces offirst PCB layer 90 utilizing photolithographic processing techniques andmetallization techniques known in the art. Once first PCB layer 90 hascircuit pattern 101 formed on one or both exposed surfaces thereof,first PCB layer 90 and each tab 92 can be singulated from panel 98,especially disposable part 96, and utilized as is. If desired, however,one or more additional layers of electrically insulative coating andcircuit patterns can be formed over circuit pattern 101, with thevarious layers of circuit patterns interconnected in a desired mannerutilizing conventional processes. Thereafter, first PCB layer 90 andeach tab 92 can be singulated from panel 98.

With reference to FIGS. 10 and 11, if desired, panel 98 can be laminatedto a panel 106 in a manner known in the art with first PCB layer 90laminated in registry with a second PCB layer 102 of panel 106 to form amulti-layer PCB assembly 104, shown best in FIGS. 11-13. Second PCBlayer 102 is part of panel 106 that includes tabs 108 and disposablepart 110. One or more tabs 108 can each include a mounting hole 112 thatcan be utilized to couple tab 108 to appropriate mechanical hardware orelectrical circuitry. In a manner similar to PCB layers 30 and 42 andtabs 36 and 48, respectively, second PCB layer 102 and tabs 108 can beformed from an electrically conductive sheet coated with an electricallyinsulative coating. However, the electrically insulative coating can beomitted from each tab 108 or can be removed from each tab 108 afterdeposit.

A circuit pattern 114 can be formed on one or both surfaces of secondPCB layer 102 utilizing photolithographic processing techniques andmetalization techniques known in the art. Appropriate techniques knownin the art can be utilized to form one or more electrical connectionsbetween circuit pattern 101 and circuit pattern 114.

With reference to FIG. 12, and with continuing reference to FIG. 11,next, a breaking force can be applied to each tab 92 and 108 tosingulate first and second PCB layers 90 and 102 and, hence, multi-layerPCB assembly 104, from disposable parts 96 and 110. To facilitate theapplication of a breaking force to each tab 92 and 108, tabs 92 and 108can be positioned on first and second PCB layers 90 and 102 so that theydo not overlay each other. As shown, all of each tab 92 and all of eachtab 108 remains with first and second PCB layers 90 and 102,respectively. To this end, a breaking force applied to each tab 92 andeach tab 108 causes it to break from disposable part 96 and 110,respectively. To enable each tab 92 and 108 to break cleanly fromdisposable parts 96 and 110, a break or score line can be formed at theboundary of each tab 92 and 108 and each disposable part 96 and 110 toweaken the mechanical connection therebetween. A suitable breaking forcecan be applied to each tab 92 and 108 by a mechanical press having a ramwith a suitably shaped tip for causing the breaking force to be appliedto the tab, especially the score line.

Alternatively, a breaking force can be applied to each tab 92 and 108 atthe perimeter (or edge) of first and second PCB layers 90 and 102,respectively, i.e., at the boundary between each tab 90 and 92 and firstand second PCB layers 90 and 102. Upon applying such breaking force,portions of the edges of first and second PCB layers 90 and 102 wheretabs 92 and 108, respectively, were connected become exposed. Morespecifically, separating each tab 92 and 108 from first and second PCBlayers 90 and 102, respectively, at the perimeters thereof exposesportions of the edges of the conductive sheets of first and second PCBlayers 90 and 102 where said tabs 92 and 108 were previously connected.

With reference to FIG. 13, and with continuing reference to FIGS. 11 and12, assuming that the breaking force is applied to each tab 92 and eachtab 108 causes it to break from disposable parts 96 and 110,respectively, at a suitable time one or more electrical components 120,such as, without limitation, a packaged integrated circuit, anunpackaged flip-chip integrated circuit, a resistor, a capacitor and/oran inductor can be coupled to appropriate points of circuit pattern 101and/or circuit pattern 114 of multi-layer PCB assembly 104 in a mannerknown in the art. Moreover, as shown in FIG. 14, one or more tabs 92and/or 108 can be coupled to a mounting fixture 122 or an electricalfixture, such as a power supply 124. Since each tab 92 is part of anelectrically conductive sheet 130 associated with first PCB layer 90,and since each tab 108 is part of an electrically conductive sheet 132associated with second PCB layer 102, connecting one or more tabs 92 toone terminal of power supply 124 and connecting one or more tabs 108 tothe other terminal of power supply 124 biases electrically conductivesheets 130 and 132 accordingly. The provisioning of electrical power toelectrically conductive sheets 130 and 132 in this manner simplifies theprovisioning of electrical power to each electrical component, e.g.,electrical component 120, coupled to one or both outward facing surfacesof multi-layer PCB assembly 104.

In addition, other electrical components, such as one or more capacitors134, can be connected between adjacent pairs of tabs 92 and 108. Theinclusion of one or more capacitors 134 between adjacent pairs of tabs92 and 108 reduces the need to install filter capacitors on one or bothof the outward facing surfaces of multi-layer PCB assembly 104 toprovide electrical filtering for electrical components disposed thereon.

Like the distal end of exemplary tab 36, the distal end 136 of each tab92 and the distal end 137 of each tab 108 includes an exposed edge ofelectrically conductive sheet 130 and 132, respectively. In addition,all or part of the top surface and/or bottom surface of the electricallyconductive sheets 130 and 132 associated with adjacent pairs of tabs 92and 108, respectively, can be exposed in order to facilitate theconnection of electronic components, such as capacitors 134,therebetween.

Multi-layer PCB assembly 104 includes one surface of the electricallyinsulative coating of first PCB layer 90 laminated directly to onesurface of the electrically insulative coating of second PCB layer 102as shown in FIG. 13. If desired, however, an insulating interlayer 140can be provided between first and second PCB layers 90 and 102 as shownin FIG. 15. Specifically, one surface of first PCB layer 90 can belaminated to one surface of insulating interlayer 140 while the othersurface of insulating interlayer 140 can be laminated to one surface ofsecond PCB layer 102.

One or more conductors 142, such as small conductive posts, can protrudethrough insulating interlayer 140 for connecting one or more points ofcircuit pattern 101 on first PCB layer 90 to one or more points ofcircuit pattern 114 on second PCB layer 102. Since conductors, such asconductor 142, are known in the art, details regarding the use of suchconductors will not be described herein.

While the use of insulating interlayer 140 has been described inconnection with first and second PCB layers 90 and 102, it is to beappreciated that an insulating interlayer, like insulating interlayer140, can be utilized with multi-layer PCB assembly 60, shown in FIG. 5,in the same manner that insulating interlayer 140 is used withmulti-layer PCB assembly 104, shown in FIG. 15. Specifically, onesurface of each instance of first PCB layer 30 can be laminated to asurface of an insulating interlayer, like insulating interlayer 140,while the other surface of the insulating interlayer can be laminated toone surface of an instance of second PCB layer 42 to form an embodimentof multi-layer PCB assembly 60 that includes the insulating interlayerbetween first and second PCB layers 30 and 42.

In FIGS. 3-5 and 9-12, each PCB layer 30, 42, 90 and 102 is illustratedas including one or more conventional plated through-holes (or vias)therethrough. Each such conventional plated through-hole (or via)includes a so-called “land” L therearound on each end thereof thatterminates on an exposed surface of the printed circuit board layer(see, e.g., FIG. 2). The use of land L around each end of a platedthrough-hole (or via) that terminates on an exposed surface of a printedcircuit board layer enables the conductive material in the via to beelectrically connected to a conductor, e.g., a conductive trace or line,on the surface of the printed circuit board in a manner known in theart. One problem with the use of land L around each end of a platedthrough-hole or via that terminates on an exposed surface of a printedcircuit board layer is that the additional conductive material utilizedto form land L provides increased opportunities for forming electricalshorts with adjacent conductive lines or lands L during installation ofelectrical components on the printed circuit board layer. Moreover, theuse of lands L decrease the available density of conductor lines andlands on the printed circuit board layer. More specifically, printedcircuit board layers are manufactured in accordance with rules regardingminimum spacing between edges of adjacent conductors, such as lands Land conductive lines. Accordingly, eliminating the land L around eachexposed end of a through-hole or via enables an adjacent structure, suchas an adjacent land L or an adjacent conductive line, to be moved closerto the landless through-hole or via without violating the minimumspacing rule. Accordingly, it would be desirable to eliminate the use ofa land L around each exposed end of a through-hole or via.

With reference back to FIG. 1, a method of forming printed circuit boardlayer 2 with a landless through-hole or via will now be described. Asdescribed above in connection with FIG. 1, printed circuit board layer 2includes an electrically conductive sheet or foil 4 that is formed froma copper foil, an iron-nickel alloy, or combinations thereof. In onedesirable embodiment, electrically conductive sheet 4 is formed ofInvar. Sheet 4 can have one or more through-holes or vias 6 that extendthrough sheet 4.

With reference to FIGS. 16 and 17 and with continuing reference to FIG.1, sheet 4, including each through-hole 6 therein, is optionallyconformally coated with a copper layer 144. Desirably, copper layer 144is electrodeposited on sheet 4. However, this is not to be construed aslimiting the invention.

The use of copper layer 144 is particularly advantageous when sheet 4 isformed from a material other than copper in order to avoid mismatchesbetween the thermal coefficient of expansion of the material formingsheet 4 and the thermal coefficient of expansion of materials depositedover copper layer 144 or electrical components mounted to printedcircuit board layer 2.

Next, sheet 4, or copper layer 144 if present, is conformally coatedwith insulative material to form coating 8. Desirably, the insulativematerial forming coating 8 is initially electrodeposited on sheet 4 orcopper layer 144, if present. Electrodepositing this insulative materialproduces a substantially uniform layer that conforms to the surfaces andedges of sheet 4 or copper layer 144, if present. It has been observedthat this substantially uniform layer of electrodeposited insulativematerial, however, has a relatively rough surface that is not desirablefor forming a circuit pattern, e.g., circuit pattern 146, thereon.Accordingly, after the insulative material has been electrodeposited,PCB layer 2 is heated to an elevated temperature sufficient to cause theinsulative material to wholly or partially melt. Upon melting, theinsulative material deposited on the opposing surfaces of sheet 4 orcopper layer 144, if present, flows and levels thereby becomingsufficiently flat so that when cooled provides a suitably smooth anduniform surface for forming circuit pattern 146 thereon. Melting theinsulative material also enables it to flow around the edges of eachthrough-hole 6. More specifically, melting the insulative materialcauses the shape of the insulative material in through-hole 6 to changefrom its conformally coated shape (shown in phantom) to the shape shownin cross section in FIG. 17. When cooled back to a solid, the insulativematerial inside each through-hole 6 retains the shape substantially asshown in FIG. 17.

Upon cooling, the insulative material forms coating 8. Coating 8includes insulating top layer 10 which covers top surface 12 of sheet 4or top surface 148 of copper layer 144, if present, insulating bottomlayer 14 which covers a bottom surface 16 of sheet 4 or a bottom surface150 of copper layer 144, if present, an insulating edge layer 18 (shownbest in FIG. 1) which covers an edge 20 of sheet 4, and, for eachthrough-hole 6, an insulating through-hole layer 152 which covers aninterior surface 154 of sheet 4 or an interior surface 156 of copperlayer 144, if present.

As can be seen, once coating 8, especially insulating through-hole layer152, is formed, the surface of insulating through-hole layer 152converges from a position adjacent top layer 10 to a positionintermediate top layer 10 and bottom layer 14 and diverges from theposition intermediate top layer 10 and bottom layer 14 to a positionadjacent bottom layer 14.

As shown in the cross section of through-hole 6 in FIG. 17, one side ofinsulating through-hole layer 152, has an arcuate outline from theposition intermediate top layer 10 and bottom layer 14 to either theposition adjacent top layer 10 or bottom layer 14. Moreover, as shown inthe cross section of through-hole 6 in FIG. 17, opposing sides ofinsulating through-hole layer 152 have an outline generally in the shapeof a hyperbola.

Once coating 8 is formed, a layer of copper is formed, e.g.,electrodeposited, on coating 8, i.e., on top layer 10, bottom layer 14,insulating edge layer 18, and each insulating through-hole layer 152.Because insulating through-hole layer 152 has the form shown in FIG. 17,the electrodeposited copper on coating 8 conforms to the arcuate surfaceof insulating through-hole layer 152. In other words, the copperelectrodeposited on coating 8 conformally coats coating 8, especiallythe arcuate surface of insulating through-hole layer 152.

Next, the copper electrodeposited on coating 8 can be patterned andetched in a manner known in the art to define circuit pattern 146thereon. Exemplary circuit pattern 146 includes conductive traces158-164 on top layer 10, conductive traces 166 and 168 on bottom surface14 and one or more through-hole conductors 170 on the surface of eachinsulating through-hole layer 152. As shown in FIG. 17, through-holeconductor 170 has a substantially uniformed thickness.

Opposing sides of the interior surface of through-hole conductor 170have a minimum diameter D1. The arcuate surface of insulatingthrough-hole layer 152 enables electrical connection to be establishedbetween through-hole conductor 170 and conductive traces 160, 162, 166and 168 without the need for a land L, shown in phantom in FIG. 16.

With reference to FIGS. 18 and 19, and with continuing reference toFIGS. 1, 16 and 17, if desired, instead of through-hole 6 including asingle through-hole conductor 170, through-hole 6 includes a pluralityof electrically isolated through-hole conductors 170-1, 170-2, etc.,formed on insulating through-hole layer 152. Each through-hole conductor170-1, 170-2, etc., can be utilized to electrically connect a conductivetrace defined on top layer 10 to a conductive trace defined on bottomlayer 14. For example, through-hole conductor 170-1 can be utilized toelectrically connect conductive trace 160 and conductive trace 166disposed on top layer 10 and bottom layer 14, respectively, of coating8. Similarly, through-hole conductor 170-2 can be utilized toelectrically connect conductive trace 162 and conductive trace 168disposed on top layer 10 and bottom layer 14, respectively, of coating8.

The ability to form a plurality of electrically isolated through-holeconductors 170 on insulating through-hole layer 152 is facilitated bythe arcuate shape of insulating through-hole layer 152 and, thereby, thearcuate shape of the copper electrodeposited on insulating through-holelayer 152. More specifically, the arcuate shape of the copperelectrodeposited on insulating through-hole layer 152 enablesphotoresist to be deposited thereon and then patterned and etched in amanner known in the art. Thereafter, unhardened photoresist and thecopper underlying said unhardened photoresist are removed by means knownin the art, such as chemical etching, to define the plurality ofthrough-hole conductors 170-1, 170-2, etc., in through-hole 6.Thereafter, hardened photoresist can be removed by means known in theart.

As shown best in FIG. 18, removing portions of the copper deposited oninsulating through-hole layer 152 to define the plurality ofthrough-hole conductors 170 in through-hole 6 results in through-hole 6having a minimum diameter D1 between the surfaces of opposingthrough-hole conductors 170. In contrast, opposing surfaces ofinsulating through-hole layer 152 where the electrodeposited copper hasbeen removed will have a second diameter D2 that is larger than diameterD1.

The photoresist utilized to define the plurality of through-holeconductors 170 in through-hole 6 is desirably an electrodepositedphotoresist that conformally coats the copper electrodeposited oninsulating through-hole layer 152 of through-hole 6. Suitable exemplaryelectro-depositable photoresists are disclosed in U.S. Pat. No.6,560,053 to Kahle, II et al.; U.S. Pat. No. 5,733,479 to Kahle, II etal.; U.S. Pat. No. 5,721,088 to Martin et al.; and U.S. Pat. No.6,100,008 to McMurdie, which are incorporated herein by reference.

The combination of the electrodeposited photoresist on the arcuatesurface of the copper electrodeposited on insulating through-hole layer152 of through-hole 6 facilitates exposure of the photoresist to asuitable curing radiation in order to define the plurality ofelectrically isolated through-hole conductors 170 on insulatingthrough-hole layer 152. In contrast, the vertical surface of a prior artthrough-hole limits or prevents uniform exposure of the photoresist inthe through-hole to curing radiation, especially exposure to collimatedlight that may be utilized to define one or more conductive traces, orany other portion of a circuit pattern, on top layer 10 and bottom layer14 of coating 8.

Two or more printed circuit board layers 2 described above in connectionwith FIGS. 16-19 can be utilized to form a multi-layer printed circuitboard assembly, like multi-layer PCB assembly 60 or 104, with or withoutinsulating interlayer 140 sandwiched between two or more adjacentprinted circuit board layers 2. Like printed circuit board layers 40,52, 90 and 102, printed circuit board layer 2 shown in FIGS. 16-19 canbe connected to a disposable part of a panel via one or more tabs, liketabs 36, 48, 92 or 108, and can be singulated from the panel in any oneof the manners described above in connection with printed circuit boardlayers 40, 52, 90 and 102.

As can be seen, the present invention provides a printed circuit boardhaving one or more printed circuit board layers each of which has aconductive plane that extends to the edge of the printed circuit boardbut which is substantially, but not completely, covered by an insulatingmaterial. The edge of the conductive layer not covered by the insulatingmaterial is positioned on the edge of the circuit board layer or a tabwhich is utilized to couple the circuit board layer to a disposable partof a larger panel that the printed circuit board layer is formed fromduring fabrication. The exposed edge of the conductive layer becomesexposed upon singulating the printed circuit board layer from thedisposable part of the panel.

The conductive layer of each circuit board layer can serve the dualpurpose of conducting heat away from electrical components disposed onone or both surfaces of the printed circuit board or printed circuitboard layer and providing power or ground to the electrical components.

The present invention also provides a printed circuit board layer havingone or more landless through-holes therethrough. Desirably, in crosssection, one side of the interior surface of each through-hole has anarcuate outline from a position intermediate the ends thereof to eitherthe position adjacent one end thereof or the position adjacent the otherend thereof. In one desirable embodiment, in cross section, opposingsides of the interior surface of the through-hole have an outlinegenerally in the shape of a hyperbola. Because the interior surface ofone side of each through-hole has an arcuate outline in cross section,each through-hole can include a single through-hole conductor extendingtherethrough or a plurality of electrically isolated through-holeconductors extending therethrough. The ability to form a number ofelectrically isolated through-hole conductors in a single through-holeenables a reduction in the number of through-holes through the circuitboard that are required for passing signals between opposing surfaces orlayers thereof. Thus, the use of landless through-holes or vias inaccordance with the present invention is capable of reducing the numberof through-holes or vias required in a printed circuit board to passsignals between opposing surfaces of the printed circuit board.

The present invention has been described with reference to the preferredembodiments. Obvious modifications and alterations will occur to othersupon reading and understanding the preceding detailed description. Forexample, multi-layer PCB assembly 60 was described as being formed bylaminating together PCB layers 30 and 42 with or without an insulatinglayer, like insulating interlayer 140, laminated between PCB layers 30and 42. However, a multi-layer PCB assembly can be formed from three ormore PCB layers laminated together, with or without an insulating layer,like insulating interlayer 140, laminated between one or more adjacentpairs of PCB layers, with the circuit pattern of each pair of adjacentPCB layers electrically connected in a desired manner. Moreover, anelectrical component, e.g., capacitor 134, was described as beingconnected to tabs 92 and 108 of adjacent PCB layers 90 and 102 ofmulti-layer PCB assembly 104. However, an electrical component can beconnected between tabs of adjacent or non-adjacent PCB layers of amulti-layer PCB assembly having three or more PCB layers. It is intendedthat the invention be construed as including all such modifications andalterations insofar as they come within the scope of the appended claimsor the equivalents thereof.

1. A multi-layer circuit board comprising: a plurality of circuitboards, each circuit board comprising an electrically conductive sheetcoated with an insulating top layer covering one surface of theconductive sheet, an insulating bottom layer covering another surface ofthe conductive sheet, an insulating edge layer covering an edge of theconductive sheet and a circuit pattern defined on an outward facingsurface of at least one of the top layer and bottom layer; and aninsulating interlayer sandwiched between a top layer of a first circuitboard of the plurality of circuit boards and a bottom layer of a secondcircuit board of the plurality of circuit boards.
 2. The circuit boardof claim 1, wherein the insulating edge layer includes at least oneopening where at least part of the edge of the conductive sheet isexposed.
 3. The circuit board of claim 1, further including at least oneelectrical conductor electrically connecting the circuit patterns on thefirst and second circuit boards by way of the insulating interlayer. 4.The circuit board of claim 1, wherein: the circuit pattern of one of thecircuit boards includes at least one electrical conductor on the toplayer of the one circuit board and at least one electrical conductor onthe bottom layer of the one circuit board; and a through-hole or viaextends through the one circuit board, the through-hole having anelectrical conducting interior surface extending therethroughelectrically connecting the one electrical conductor on the top layer ofthe one circuit board and the one electrical conductor on the bottomlayer of the one circuit board, the electrical conducting interiorsurface electrically isolated from the electrically conductive sheet byan insulating through-hole layer.
 5. The circuit board of claim 4,wherein the interior surface of the through-hole converges from aposition adjacent the top layer of the one circuit board to a positionintermediate the top layer and the bottom layer of the one circuit boardand diverges from the position intermediate the top layer and the bottomlayer of the one circuit board to a position adjacent the bottom layerof the one circuit board.
 6. The circuit board of claim 5, wherein, incross section, the interior surface of one side of the through-hole hasan arcuate outline from the position intermediate the top layer and thebottom layer to either the position adjacent the top layer or theposition adjacent the bottom layer.
 7. The circuit board of claim 6,wherein, in cross section, opposing sides of the interior surface of thethrough-hole have an outline generally in the shape of a hyperbola. 8.The circuit board of claim 1, wherein: the circuit pattern of one of thecircuit boards includes a plurality of electrical conductors on the toplayer of the one circuit board and a plurality of electrical conductorson the bottom layer of the one circuit board; and a through-hole or viaextends through the one circuit board, the through-hole having aplurality of through-hole conductors extending therethrough, eachthrough-hole conductor electrically isolated from each otherthrough-hole conductor, each through-hole conductor electricallyconnected to at least one electrical conductor on the top layer or thebottom layer of the one circuit board.
 9. The circuit board of claim 8,wherein an interior surface of the through-hole converges from aposition adjacent the top layer of the one circuit board to a positionintermediate the top layer and the bottom layer of the one circuit boardand diverges from the position intermediate the top layer and the bottomlayer of the one circuit board to a position adjacent the bottom layerof the one circuit board.
 10. The circuit board of claim 9, wherein, incross section, either one of the through-hole conductors or one side ofthe insulating through-hole layer disposed between a pair ofthrough-hole conductors has an arcuate outline from the positionintermediate the top layer and the bottom layer to either the positionadjacent the top layer or the position adjacent the bottom layer. 11.The circuit board of claim 10, wherein the cross section of either theone through-hole conductor or the one side of the insulatingthrough-hole layer disposed between a pair of through-hole conductorshas an outline generally in the shape of one side of a hyperbola.
 12. Amethod of forming a multi-layer circuit board comprising: (a) providinga plurality of circuit boards, each circuit board comprising anelectrically conductive sheet conformally coated with an insulatingmaterial; (b) forming a first circuit on one of the circuit boards; (c)forming a second circuit on another of the circuit boards; and (d)laminating the plurality of circuit boards together with an insulatinginterlayer disposed between the one circuit board and the other circuitboard, and with the first and second circuits electrically connected byway of the insulating interlayer.
 13. The method of claim 12, whereineach circuit comprises at least one conductor.
 14. The method of claim12, wherein the conformally coated insulating material includes at leastone opening where at least part of an edge of the conductive sheet isexposed.
 15. The method of claim 14, wherein the one opening is on a tabthat extends from the circuit board either within or outside a perimeterof the circuit board.
 16. The method of claim 12, further including:conformally coating a through-hole or via in the conductive sheet of theone circuit board with the insulating material; and forming at least onethrough-hole conductor on at least a portion of the insulating materialin the through-hole, with the one through-hole conductor electricallyconnected to at least one conductor of the first circuit formed on oneside of the first circuit board and to at least one conductor of the onecircuit formed on the other side of the one circuit board.
 17. Themethod of claim 16, further including forming a plurality ofelectrically isolated through-hole conductors on the insulating materialin the through-hole, with each through-hole conductor electricallyconnected to at least one conductor of the first circuit formed on oneside or on the other side of the first circuit board.
 18. The circuitboard of claim 17, wherein an interior surface of the through-holeconverges from a position adjacent a top surface of the one circuitboard to a position intermediate the top surface and the bottom surfaceof the one circuit board, and diverges from the position intermediatethe top surface and the bottom surface of the one circuit board to aposition adjacent the bottom surface of the one circuit board.
 19. Thecircuit board of claim 18, wherein, in cross section, one side of thethrough-hole has an arcuate outline from the position intermediate thetop surface and the bottom surface to either the position adjacent thetop surface or the position adjacent the bottom surface.
 20. The circuitboard of claim 19, wherein the cross section of the one side of thethrough-hole has an outline generally in the shape of one side of ahyperbola.
 21. A circuit board comprising: an electrically conductivesheet coated with an insulating top layer covering one surface of theconductive sheet, an insulating bottom layer covering another surface ofthe conductive sheet and an insulating edge layer covering an edge ofthe conductive sheet; an electrical conductor on the top layer of thecircuit board and an electrical conductor on the bottom layer of thecircuit board; and a through-hole or via through the circuit board, thethrough-hole having a through-hole conductor extending therethroughelectrically connecting the electrical conductor on the top layer andthe electrical conductor on the bottom layer, the through-hole conductorelectrically isolated from the electrically conductive sheet by aninsulating through-hole layer.
 22. The circuit board of claim 21,wherein the insulating edge layer includes at least one opening where atleast part of the edge of the conductive sheet is exposed.
 23. Thecircuit board of claim 21, wherein an interior surface of thethrough-hole converges from a position adjacent the top layer of thecircuit board to a position intermediate the top layer and the bottomlayer of the circuit board, and diverges from the position intermediatethe top layer and the bottom layer of the circuit board to a positionadjacent the bottom layer of the circuit board.
 24. The circuit board ofclaim 23, wherein, in cross section, one side of the interior surface ofthe through-hole has an arcuate outline from the position intermediatethe top layer and the bottom layer to either the position adjacent thetop layer or the position adjacent the bottom layer.
 25. The circuitboard of claim 24, wherein, in cross section, opposing sides of theinterior surface of the through-hole have an outline generally in theshape of a hyperbola.
 26. The circuit board of claim 21, furtherincluding a plurality of electrical conductors on the top layer of thecircuit board and a plurality of electrical conductors on the bottomlayer of the circuit board, wherein: the through-hole includes aplurality of through-hole conductors extending therethrough; eachthrough-hole conductor is electrically isolated from each otherthrough-hole conductor; and each through-hole conductor is electricallyconnected to at least one electrical conductor on the top layer and atleast one electrical conductor on the bottom layer.
 27. The circuitboard of claim 26, wherein an interior surface of the through-holeconverges from a position adjacent the top layer of the circuit board toa position intermediate the top layer and the bottom layer of thecircuit board and diverges from the position intermediate the top layerand the bottom layer of the circuit board to a position adjacent thebottom layer of the circuit board.
 28. The circuit board of claim 27,wherein, in cross section, the interior surface of the through-hole hasan arcuate outline from the position intermediate the top layer and thebottom layer to either the position adjacent the top layer or theposition adjacent the bottom layer.
 29. The circuit board of claim 28,wherein the cross section of the through-hole has an outline generallyin the shape of one side of a hyperbola.
 30. A method of forming acircuit board comprising: (a) providing a circuit board having athrough-hole or via therethrough; (b) conformally coating theelectrically conductive sheet, including an interior surface of thethrough-hole, with an insulating material; (c) forming a conductor onone side of the conformally coated electrically conductive sheet; (d)forming another conductor on the other side of the conformally coatedelectrically conductive sheet; and (e) forming a through-hole conductoron the insulating material in the through-hole, the through-holeconductor electrically connecting the conductor on the one side of theconformally coated electrically conductive sheet and the conductor onthe other side of the conformally coated electrically conductive sheet.31. The method of claim 30, wherein: step (c) includes forming aplurality of conductors on the one side of the conformally coatedelectrically conductive sheet; step (d) includes forming a plurality ofconductors on the other side of the conformally coated electricallyconductive sheet; step (e) includes forming a plurality of through-holeconductors on the insulating material in the through-hole; eachthrough-hole conductor is electrically isolated from each otherthrough-hole conductor; and each through-hole conductor is electricallyconnected to at least one conductor on the one side of the conformallycoated electrically conductive sheet and at least one conductor on theother side of the conformally coated electrically conductive sheet. 32.The method of claim 31, wherein the conformally coated insulatingmaterial includes at least one opening where at least part of an edge ofthe conductive sheet is exposed.
 33. The method of claim 32, wherein theat least part of the edge of the conductive sheet is on a tab thatextends from the circuit board either within or outside a perimeter ofthe circuit board.
 34. The circuit board of claim 30, wherein aninterior surface of the through-hole converges from a position adjacentthe one side of the conformally coated, electrically conductive sheet toa position intermediate the one side and the other side of theconformally coated electrically conductive sheet, and diverges from theposition intermediate the one side and the other side of the conformallycoated electrically conductive sheet to a position adjacent the otherside of the conformally coated electrically conductive sheet.
 35. Thecircuit board of claim 34, wherein, in cross section, one side of theinterior surface of the through-hole has an arcuate outline from theposition intermediate the one side and the other side to either theposition adjacent the one side or the position adjacent the other side.36. The circuit board of claim 35, wherein the cross section of the oneside of the interior surface of the through-hole has an outlinegenerally in the shape of one side of a hyperbola.